The present invention relates to embossed films obtained from ethylene-propylene copolymers, and a process and apparatus for producing the films.
In embossing the film, sunken and relief patterns are formed on the surface of the film. Usually, these patterns are regular, small and shallow. As a result of embossing, the flexibility of the film is increased, and the film is given a texture akin to that of textile fabrics.
In the past, embossed films having a thickness approaching 25 to 30microns have been obtained by blow-extruding a tubular web from a radical polymerization low-density polyethylene, cutting the tubular web longitudinally into two films having a thickness approaching 25 to 30 microns, and then embossing the two films. The embossing has been conducted by heating the film and then applying the film, by means of a pressure roll, to an embossing roll bearing incised or relief patterns. U.S. Pat. No. 3,950,480 describes such a process wherein the film passes into a heating region, and then onto an embossing roll.
U.S. Pat. No. 3,857,144 describes an embossing method wherein a blow-extruded tubular web is pinched together to form a double film, embossing the double film, and then separating the embossed, double film into its two parts by an air blast. The cold-embossing utilized in this process facilitates the separation. The resulting product is used for making bags.
Similarly, Luxembourg Pat. No. 44,493, and British Pat. No. 909,326 also disclose embossing a double-thickness film obtained from a flattened tubular web. Embossing is effected under conditions that make it easy to separate the double-thickness film into two single-thickness films.
British Pat. No. 1,087,036 discloses embossing a flat film extruded from a mixture of at least two different types of thermoplastic resins.
A major deficiency in the prior art is that it is very difficult under industrial conditions (several hours of uninterrupted blow-extrusion operation) to obtain very thin embossed films (less than 25 microns) from polyethylene films obtained by the radical mechanism.